OpenBSD can be installed from files on a partition dedicated to another operating system. You could install Windows XP in the first 7GB of your hard drive, download the distribution directory (or desired files thereof) into a directory on your Windows install, and use that as an installation source. Here, we're going to install OpenBSD from files downloaded on a Windows NT 4.0 install and stored in the directory c: obsd.
During the installation dialog, you will see the familiar installation set selection question:
Sets can be located on a (m)ounted filesystem; a (c)drom, 1 (d)isk or (t)ape device; or a (f)tp, (n)fs or (h)ttp server. Where are the install sets you want to use? (m, c, f, etc.) d
The 1 disk option allows you to install from an existing disk. Choose it, and you'll see the following menu:
Available disks are: sd0 sd1 wd0. Which one contains the install sets? (or done) [sd0]
That installer sure likes to assume drive sd0, doesn't it? My Windows install is on drive wd0, so enter that. You'll be shown a complete list of the partitions on this drive.
The following partitions have been found on wd0: a: 1024002 8193150 4.2BSD 1024 8192 16 # (Cyl. 8128*- 9143) b: 1208592 9217152 swap # (Cyl. 9144 - 10342) c: 39179952 0 unused 0 0 # (Cyl. 0 - 38868) d: 12582864 10425744 4.2BSD 1024 8192 16 # (Cyl. 10343 - 22825) e: 2097648 23008608 4.2BSD 1024 8192 16 # (Cyl. 22826 - 24906) f: 14060214 25106256 4.2BSD 1024 8192 16 # (Cyl. 24907 - 38855*) i: 8193087 63 MSDOS 1 # (Cyl. 0*- 8128*) Partition? [a]
The only annoying thing here is that you have already created OpenBSD partitions by this point, and you'll have to sort through them all. Still, the 1 MSDOS file system is easy to find amidst all this. It's on partition "i," so enter that.
As OpenBSD cannot identify all sorts of file systems automatically, you will have to choose the file system type on that partition. The "default" should work for most cases, but you may have to explicitly enter "msdos" if you have a problem. You can easily install from MSDOS, Linux, and UFS partitions with the installer.
The following filesystem types are supported: default (deduced from the disklabel) ffs msdos Which filesystem type? [default]
The installer will then ask you which directory you placed the installation sets on.
Enter the pathname where the sets are stored (or '?') /obsd
At this point, the installer will pick up the installation sets, and you can proceed normally.